1. Field of the Invention
The present invention relates to an inkjet printing apparatus which includes an inkjet printing head configured to eject ink and moves the inkjet printing head relative to a print medium to perform printing on the print medium by means of ink droplets ejected from a liquid ejecting part.
2. Description of the Related Art
For an inkjet printing apparatus, improvements in image quality and colorfulness of a printed image have been required in recent years. Consequently, for the purpose of achieving superior fineness of a printing head, an inkjet printing apparatus in recent years has come to have a largely increased number of ejection ports arrayed at a high density, and thereby to eject smaller ink droplets. Along with these changes, a phenomenon has become increasingly pronounced in which, when ink ejected from a large number of nozzles as printing is performed, an extremely fine ink mist accompanying ink droplets forming a printed image is scattered into a spray-like condition.
An ink mist scattered between a printing head of an inkjet printing apparatus and a print medium adheres to constituent elements of the printing apparatus, such as a drive mechanism. Such adherence of the ink mist to the constituent elements of the printing apparatus disturbs normal ink ejection, and therefore is a problem that must be addressed in accomplishing printing of high image quality. There are two possible approaches as countermeasures against troubles like this caused by an ink mist. One is an approach for reducing generation of the mist itself by employing an appropriate ink formula or drive method. The other is an approach for reducing adherence of an ink mist to the print medium and to the constituent elements of the printing apparatus by controlling behavior of the mist between the printing head and the print medium.
In the former one of these two approaches, it is known that generation of minute ink droplets tends to be suppressed by an ink formula capable of increasing ink viscosity. However, there is a trade-off relationship between ink viscosity and an ink ejection speed. It can be safely said that development has not yet been achieved for ink capable of suppressing generation of a mist even with an ejection speed kept high enough to achieve a high image quality. As an example based on the latter approach, there is an inkjet printing apparatus including a flow regulator installed in a front side of the printing head in a travelling direction of a carriage, and being capable of preventing generation of a complex airflow by using the flow regulator and thereby reducing adherence of an ink mist to the driving mechanism.
However, a front shape of the carriage in the scanning direction is not the only factor influencing an airflow between the printing head of the inkjet printing apparatus and the print medium. Under a printing condition with a high drive frequency per nozzle for such a case as solid printing with ink of only one color, momentum held by ejected ink droplets are transmitted to the air, whereby a complex airflow curling up from the print medium toward the printing head is caused between the printing head and the print medium.
This airflow heading for the printing head will be described below. When ink droplets are ejected from the printing head toward the print medium, airflows from the printing head toward the print medium are generated in association with movements of the ink droplets at first. Then, when reaching the print medium, these airflows turn around by bumping into the print media, and then form airflows oppositely heading toward the printing head. Such an airflow field is inevitably formed when ink droplets are ejected, and therefore, cannot be controlled with the flow regulator in the front side of the carriage in the scanning direction.
Such airflows heading for the printing head cause an ink mist to adhere to a face surface which is an ink ejecting surface of the printing head. During printing, ink is repeatedly ejected and the ink mist adhering to the face surface is accumulated, whereby wetting of ink attributable to the mist is formed around nozzle arrays. This wetting causes color mixing of ink and improper ejection, and therefore is as a factor of image quality reduction.
Conceivable countermeasures for solving this problem are restoration operations such as suction and wiping at a home position. When time required for the printing and increase of wasted ink are taken into consideration, however, it is not preferable to frequently perform such a restoration operation. In an inkjet printing apparatus, these airflows curling up between the face surface and the print medium are a stubborn obstacle to simultaneous achievement of high image quality and high-speed printing.
Here, when adherence of the mist to the face surface is reduced, a larger amount of the mist is scattered toward an entirety of a housing from a region between the printing head and the print medium; however, this problem can be effectively handled by use of a mist collecting mechanism installed in the housing.
In Japanese Patent Laid-open No. 2004-330637, as a constituent element which controls behavior of ink mist, fans are installed in front and back, in a scanning direction of a carriage, of a region between a printing head and a print medium. However, in such a method for controlling an airflow in a scanning direction of a carriage, a nozzle array following a preceding nozzle array in the scanning direction receives an influence of airflows formed by the preceding nozzle array. Consequently, it is difficult to give uniform air flowing conditions to all of the plural nozzle arrays lined up in the carriage scanning direction. In inkjet printing, an inflow of air between the printing head and the print medium influences landing positions of ink droplets, and therefore relates to image quality to a large extent. In order to achieve both reduction of adherence of an ink mist to a face surface and high image quality, it is preferred to make inflows of air around the plural provided nozzle arrays even and uniform.
It is known that airflows curling up between the printing head and the print medium are attenuated relative to an increase in an inflow of air flowing into a space between the printing head and the print medium. However, there is no effective means for effectively increasing an air flowing into the space between the printing head and the print medium. For this reason, airflows cannot be prevented from heading for the printing head, whereby print quality is reduced due to such reasons as adherence of an ink mist to the face surface.